1. Field of the Invention
The present invention relates to simple transmissions utilizing compound countershafts and in particular relates to simple transmissions of the floating mainshaft, multiple countershaft type wherein the countershafts are compounded.
2. Description of the Prior Art
Simple transmissions, that is, transmissions utilizing a one piece mainshaft, are well known in the prior art. Transmissions utilizing either simple or compound mainshafts in connection with multiple countershafts wherein either the mainshaft gears or the countershaft gears are mounted in a radially floating manner relative to the other gears are well known in the prior art. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,255,644; 3,283,613; 3,335,616; 3,349,635; 3,378,214; 3,500,695; and 3,648,546.
The prior art transmissions, particularly those transmissions utilizing a floating mainshaft in connection with multiple countershafts, have proven to be highly acceptable. However, to achieve a sufficiently large range of available gear ratios, it has generally been necessary to utilize a compound transmission. Such transmissions generally comprise a main transmission and an auxiliary transmission of either the "range" type or the "splitter" type or a combination thereof as is well known in the prior art. Such transmissions are highly effective and commercially successful, especially for use in heavy duty vehicles wherein a large range of ratios is required and a large number of individual gear ratios is required. Such heavy duty compound transmissions typically have 9, 10, 12, 13 or more forward gear ratios.
There has, however, developed a need for transmissions having a greater range of ratios and a greater number of ratios than is normally available in a simple transmission as the center-line distances required in prior art simple transmissions to provide same would become too great yet not justifying the somewhat expensive structure and controls required for a compound transmission. The prior art devices have been unable to completely satisfactorily fill this need.